The manufacture of cylinder heads for internal combustion engines poses difficult manufacturing problems. The cylinder head of an internal combustion engine, whether a spark-driven, gasoline internal combustion engine or a compression ignition diesel engine, is a complex article of manufacture with many requirements. The cylinder head generally closes the engine cylinders and contains the many fuel explosions that drive the internal combustion engine, provides separate passageways for the air intake to the cylinders and for the engine exhaust, and provides a separate passageway for coolant to remove heat from the cylinder head. It is desirable that the internal walls of the cylinder head between the coolant passageways and cylinder closures and exhaust manifolds permit a reliable and effective transfer of heat from the cylinder head, and it is also important that the cylinder head include minimal metal to reduce its weight and cost.
Cylinder heads are most generally manufactured by casting them from metal alloys. The casting of the cylinder head portion that encloses the cylinders carries the intake and exhaust valves and fuel injectors and provides cavities or passageways for the air intake exhaust and coolant is formed by a plurality of core elements, including a water jacket core to form the coolant passageway. The cavities for coolant, air intake and exhaust must, of course, be formed by core elements within the mold that can be removed when the casting metal solidifies.
To provide effective cooling of the cylinder head and effective air intake and exhaust from the cylinders of the internal combustion engine, the passageways for the air intake and exhaust are best interlaced with the coolant passageways within the cylinder head. To obtain maximal output from an internal combustion engine, it is necessary that the coolant passageway formed within the cylinder heads encompass the engine exhaust with coolant. Thus, in casting the cylinder head it is necessary that the exhaust ports of the cylinder head be formed with the thinnest possible metal walls that are totally bathed in an unrestricted flow of coolant. The casting of such cylinder heads requires that a water jacket core be reliably formed with casting sand extending completely around the hole which will form the outer surface of the exhaust ports of the cylinder head.
In order to obtain water jacket cores that encompass the exhaust ports, water jacket cores have been made in two portions, with two hot-box cores, an upper hot-box core with a cavity to completely form the upper portion of the water jacket core and the lower hot-box core with a cavity to completely form the lower portion of the water jacket core. Water jacket cores have been formed by the hot-box process in which the upper core box and lower core box were each filled with a core sand including a heat-curing resin. The two core boxes, after being filled, were then placed in an oven for curing generally at temperatures on the order of 500.degree.-600.degree. F. for several minutes. Following the curing of the upper and lower portions of the water jacket cores, the upper and lower water jacket core portions were removed from their respective core boxes, and the interfacing surfaces of the upper and lower water jacket core portions were rubbed on a leveling plate, with core fins being removed for all locations. One, or both, of the interfacing surfaces of the water jacket core box portions were pressed against a plate with adhesive on it. The lower water jacket core portion was set in an assembly fixture, with its interfacing surface presented for assembly. The interfacing surface of the upper water jacket core portion was then manually positioned on the interfacing surface of the lower water jacket core portion with the adhesive therebetween, and the two portions were manually aligned. The assembled water jacket core portions were then carried through an oven at several hundred degrees to cure the adhesive.
After the adhesive had cured, the assembled water jacket core was removed from the assembly fixtures and coated with a refractory wash and again sent through the oven for curing. Upon curing of the refractory wash, the water jacket core was then ready for use in casting the cylinder head assembly, as set forth, for example, in U.S. patent application Ser. No. 07/490,809 filed Mar. 7, 1990 and now U.S. Pat. No. 5,119,881.
This prior method of manufacturing water jacket cores presented a number of problems. First, the core boxes used in this prior method were difficult to maintain and expensive to build because of their exposure to the temperatures needed to cure the core sand and adhesive. In addition, the core boxes, and the core portions within the core boxes, were susceptible to warping due to the temperature changes; the core portions removed from the cooled core boxes were frequently warped; and the surfaces formed on the water jacket core portions for locating the water jacket core within the core assembly used to cast the cylinder head were frequently out of position, resulting in variations in metal thickness within the cylinder head and a requirement to include excess metal thickness into the design of the cylinder head walls to avoid cylinder head wall portions which may be too thin. In addition, assembly of the upper and lower water jacket core portions manually introduced further unreliability and required further design compromises. Variations in operator attention, variations in adhesive viscosity and the amount of adhesive used in gluing the water jacket core portions, and unreliability in obtaining a complete coating of adhesive at the interfaces all resulted in penetration of metal during the pouring into the interface at the glue line between the upper and lower water jacket portions, and this resulted in the formation of a metal fin in the coolant passageway which would frequently prohibit coolant circulation around the exhaust port.
In addition, this prior method required the use of a large gas-fired oven to cure the core sand and adhesive, an inventory of fixtures for the assembly of the upper and lower water jacket core portions, the use of a substantial amount of production floor space and four or five men. Furthermore, the time consumed in preparation of the water jacket core portions, the application of adhesive thereto, the assembly thereof, and the adhesive cure presented a bottleneck in the cylinder head manufacturing process.